Hydration properties of vegetable foods explained by Flory-Rehner theory

In this paper we have analyzed the hydration properties of vegetable materials, namely carrots and mushrooms, by means of the Flory-Rehner theory. This is done to circumvent problems with the ill-defined concept of water holding capacity. Via this thermodynamic theory one can predict the hydration properties for a wide range of mechanical loads. The theory is compared to measurements on the hydration of the vegetable samples in centrifugation experiments. The theory predicts two contributions to the hydration properties, which are due to 1) mixing free energy of water and food ingredients, and 2) the elastic energy of the crosslinked network of cell wall materials (i.e. the dietary fibers). Via independent measurements of the moisture sorption isotherms, we have quantified of the mixing contribution, which can be described by the volume-averaged Flory-Huggins Free Volume theory. From combined analysis of centrifugation and sorption experiments, we have obtained the elastic contribution, which is shown to follows the Flory-Rehner theory. Remarkably, the cell wall materials of carrots and mushrooms show very similar elastic behavior. (C) 2013 Elsevier Ltd. All rights reserved.